So these are the bases that support the XBoat Tenders (as well as the XBoats).
That would be an easy assumption to make. They're logistics support for Express Network operations.
If a Boat shows up in system, and needs maintenance, it'll be pulled out of service and maintained at the base.
This is why the network needs to have more XBoats in stock than are actually assigned to running routes. Some of them are going to be pulled for downtime and more extensive maintenance support. My thinking is that if a particular run needs (for the sake of argument and illustration purposes) 14 XBoats jumping that circuit (1 per day, round trip 2 weeks) then there would need to be 15 XBoats assigned to that specific route so as to allow for a 1 XBoat "reserve" to be pulled from the rotation for annual overhaul maintenance at a Scout Base whenever it be needed.
This suggests several XBoat tenders per system
My assumption has always been 1 Tender per other system on the Express Network within 4 parsecs plus 1 additional Tender in reserve for maintenance rotations. That way you can always keep Tenders on station and rotate relief using the reserve Tender.
Boughene/Regina/Spinward Marches has 5 other star systems within Jump-4 of Boughene ... so Boughene ought to have 6 Tenders assigned to support Express Network operations there ... 5 on station plus 1 in reserve.
as well as spare XBoats at the Scout Base.
Correct.
It also implies that at least the XBoat part of the Scout Base is in orbit, since I don't think the tenders are streamlined.
Tenders are Close Structure configuration: 4.
XBoats are Spherical configuration: 5.
Both of these hull form factors are partially streamlined.
Scout Bases would undoubtedly have orbital highport shipyard facilities "somewhere" in the star system and will usually be somewhere other than the mainworld (usually a different planetary orbit) so as to be "out of the way" from all of the major trading traffic (and potential piracy, presumably) that may happen within a particular star system.
Perhaps the Scouts have a XBoat ferry that can pull an XBoat out of orbit for ground service. Dunno if that's worth the time.
Type-S Scout/Couriers are capable of operating as 1G maneuver tugs with 100 tons of external loading.
If a Tender is being rotated off station, any XBoats that also need to be rotated out will simply be berthed internally in the Tender for transport back to base.
If a Tender is not being rotated off station, a Type-S Scout/Courier will be assigned to maneuver tug the XBoat to/from the scout base orbital facilities.
Once you factor in external loading, Type-S Scout/Couriers make for pretty decent runabouts for both maneuver tug and also refueling duties for Tenders (so the Tenders don't need to be pulled off station to refuel) in addition to simple passenger/crew shuttling between Tenders and bases plus a lot of other little "odd jobs" that need doing.